The harm radiation has done to the Apollo crew members ______.

A．the Apollo mission was very successful
B．protection from space radiation is no easy job
C．astronauts will have deformed children or grandchildren
D．radiation is not a threat to well-protected space explores

A．it protects him against the harmful rays from space
B．it provides sufficient light for plant growth
C．it supplies the heat necessary for human survival
D．it screens off the falling meteors